to not want to let ds go home with a mum whos child is uncontrollable

[excuseme]

ds wants to go to tea with a child whos mum can't control him. He runs of, hids etc. I am worried about ds safety walking home with them

If you are genuinely concerned then your are right not to let him go.
Could you go as well?

MAke an excuse.

depends - but if ds wants to go - don't you find that the guest [as in your child] wouldn't dream of following suit because it's not their mum so he'd be fine.

Say he can't manage this time and then invite both of them to yours?

I'd make an excuse tbh (although I'm ashamed to admit that)

how old is your DS?

5